1. Field of the Invention
This invention relates generally to medical devices, and more particularly to a detection device for determining whether a tracheal tube is properly positioned within the trachea of a patient.
2. Description of Related Art
There are a number of methods used by anesthesiologists to confirm that a tracheal tube has been properly positioned within the trachea of a patient. While anesthesiologists take great care to make certain that intubation of the esophagus does not occur, it is often difficult to know contemporaneously with insertion of the endotracheal device whether the device has unintentionally been placed in the esophagus. Undiagnosed intubation of the esophagus leads, in some cases, to death of the patient. It is therefore critical that there be a simple and accurate method of determining whether a tracheal tube has been properly positioned within the trachea of a patient.
In addition to the importance of proper placement of a tracheal tube, one problem which is encountered by anesthesiologists and others is the question of whether a patient is breathing. A device which confirms both proper placement of a tracheal tube and breathing would provide a much needed tool for use by the medical community.
One device which attempts to address the tracheal tube placement problem is described in "The Einstein Carbon Dioxide Detector," 60 Anesthesiology 613 (1983). In this article, a device is described which recognizes the well established fact that gases expelled from the trachea contain CO.sub.2 while gases within the esophagus do not.
The operation of the Einstein detector device is broadly based upon a visual indication of the carbon dioxide concentration found in expired gases. The technique described in the Anesthesiology article is based on the fact that gases expired from the lungs contain between 4% and 6% CO.sub.2 whereas atmospheric air, which is expelled from the esophagus, has a negligible amount of CO.sub.2. The device utilizes an adapter connected at one end to a mucous trap. A tube connected to the trap is filled with a liquid indicator solution, and the catheter end of the trap is positioned to be well below the indicator fluid level. The adapter is attached to the endotracheal tube, and expired gases are pumped through the indicator solution and are allowed to bubble therethrough. Utilizing a cresol red and phenolphthalein solution, a gradual color change from red to yellow occurs after several seconds upon proper tracheal intubation. No color change of the solution suggests esophageal intubation.
The Einstein detector has many drawbacks. Because the gas is bubbled through a liquid indicator, expired gas must be pumped through the liquid. This, of course, requires additional equipment not usually associated with a conventional tracheal tube, such as a conduit or sample tube, a mucous trap, and of course, the liquid chemicals themselves. Liquid chemicals have their own inherent disadvantages; in particular, they are impractical because they can spill. Further, the change in color does not occur until three to five seconds after trap chamber. The Einstein CO.sub.2 detector also does not follow the breathing pattern of the patient. In other words, the indicator used by the Einstein CO.sub.2 detector is not reversible on a time frame which would enable visual confirmation of breathing. Thus, the Einstein CO.sub.2 detector is limited in its ability to provide an indication of proper or improper intubation. It does not actively detect breathing; it only detects placement.
There are, of course, a number of different types of detectors associated with intubation devices which are used in varying applications. For example, U.S. Pat. No. 3,373,735 to Gallagher, teaches a device which indicates proper placement of a tube into a patient's stomach. After the tube is inserted into the stomach of a patient, a small amount of the stomach fluid is drawn into the tube to wet a color-change indicator. When the tube is properly inserted within the stomach of a patient, the indicator will turn red. If, however, the end of the tube has been improperly placed into the lungs, the indicator would remain a blue color. This device, of course, has nothing to do with the detection of respiration.
In addition to the Einstein CO.sub.2 detector, there are other carbon dioxide detectors for both medical and nonmedical applications. In the medical area, infrared and mass spectroscopy are used as CO.sub.2 detectors. In the non-medical area, U.S. Pat. No. 3,694,164 to Guenther discloses a system for sensing the carbon dioxide content of a gas. One embodiment taught by Guenther utilizes an infrared source which is mounted a fixed distance from a cell constructed on a conductive material such as aluminum. Radiation from the infrared source is focused onto the face of the cell and covers a major portion of the face of the cell. The face of the cell contains a small aperture which is sealed by a window which transmits virtually 100% of the infrared radiation which is absorbed by pure CO.sub.2 which fills the cell. Both the inner chamber of the cell and the face of the cell are fitted with thermistors which are connected to a sensing device for detecting the differences between the temperatures of the two thermistors. The source and sensor are turned on and allowed to come to temperature equilibrium in an atmosphere virtually free of CO.sub.2, and the sensor is set to a chosen reference. Upon exposure to an atmosphere of CO.sub.2 gas, the radiation formerly absorbed by the gas in the cell is decreased, whereas that radiation absorbed by the face of the cell is affected only slightly. The temperature differential allows the user to detect the content of carbon dioxide in the cell. While this device detects CO.sub.2, it is not colorometric, it is not rapid and is not positioned in a gas stream.
In another embodiment shown in the Guenther patent, a porous impregnated surface contains a color-change indicator which changes in accordance with the carbon dioxide content. This embodiment, however, does not discuss the ability of the device to cycle from one color to another at a rate which is on the same order of magnitude as is the rate of breathing. In general, Guenther is not directed toward providing a CO.sub.2 detector for use as a medical device.
U.S. Pat. No. 3,068,073 to Stanford discloses a device for detecting the presence and determining the content of carbon dioxide in gases. The gas containing an undetermined amount of carbon dioxide is passed through a solid reagent which includes alumina carrying parent container and changes color by contact with carbon dioxide. The quantity of carbon dioxide is determined by the length of time it takes for the color indicator to change the colors. In medical applications such as determining whether the intubation of the trachea has occurred, a rapid time change is preferred. Thus, such a time-consuming procedure would not be appropriate for medical applications.
It is therefore one object of the invention to provide a CO.sub.2 indicator which is contained within the respired gas stream of a tracheal tube.
It is a further object of the invention to provide a tracheal tube having a colorimetric CO.sub.2 detector which follows the breathing pattern of a patient.